Couplings of this type are known in many different embodiments, depending on operating conditions and on the purposes which the coupling, in general, is to serve.
Where, e.g., a grinding tool is involved, it must be capable of centering the tool precisely, just as the coupling must be easy to operate with a view to replacement of the tool, either because it is worn, or where another tool is needed.
Normally, such couplings are constructed as a spindle having threads, it being possible to clamp the tool to the shaft by means of a flange and a bolt.
However, this requires partly a tool, partly a very precise machining of the surfaces or the fit between shaft and hub. The latter makes it expensive to manufacture the coupling.
Where a one-way coupling is needed, a mechanical toothed arrangement with pawls or the like will normally have to be incorporated. Such a mechanical device, too, is relatively expensive to manufacture, and it also requires maintenance.
Another coupling type of the type defined in the invention is known from DE 1750227.
This coupling comprises a driving shaft which is capable of making no, slightly driving or firmly driving contact, respectively, with a surrounding, driven hub, and a plurality of loose bodies, which extend in grooves in the exterior of the driving shaft, will be able to engage the driven shaft by means of the centrifugal force.
This coupling is vitiated by certain defects and drawbacks, which are primarily caused by the fact that the coupling is imprecise, as it may tend to be engaged and/or disengaged non-uniformly, which will have as a result that the centering is imprecise because of the uneven coupling engagement.
To this should be added the relatively large number of elements comprised by the coupling, which adds to the manufacturing costs.